chore: Deprecate connecting a Component to itself

[silvanocerza]

Calling Pipeline.connect() with the same Component both as sender and receiver will now emit a warning.

This will change in 2.7.0 and raise an exception. This change will come together with the internal Pipeline.run() rework release.

[coveralls]

Pull Request Test Coverage Report for Build 11029754959

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 52 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.09%) to 90.362%

---

Files with Coverage Reduction	New Missed Lines	%
components/classifiers/zero_shot_document_classifier.py	3	91.07%
components/generators/openai.py	3	96.43%
utils/filters.py	3	96.91%
components/evaluators/llm_evaluator.py	5	95.08%
components/generators/chat/openai.py	13	79.28%
core/pipeline/base.py	25	92.29%
<!--	Total:	52		-->

Totals
Change from base Build 10881433761:	0.09%
Covered Lines:	7341
Relevant Lines:	8124

---

💛 - Coveralls

[vblagoje]

Hey @silvanocerza looks good except that warn message is bit incongruent with PR description i.e. we say an exception will be raised in PR description while the warn message doesn't say that. Also a wording in release note is a bit odd - seems like its missing a word somewhere in "it will raise in version 2.7.0"